Search receiver with traveling wave tube



R. I. HARRISON SEARCH RECEIVER WITH TRAVELING WAVE TUBE Filed May 23,1955 July 15, 1958 RIC/MRO L HARRISON Mm/i771 W ATTORNEY SEARCH RECEIVERWITH TRAVELING WAVE TUBE Richard ll. Harrison, Bronx, Y., assignor toSylvania Electric Products Inc, a corporation of MassachusettsApplication May 23, 1955, Serial No. 510,131

15 Claims. (Cl. 259-20) The present invention relates to improvedtraveling wave tube devices, and in particular to a combined backwardwave amplifier-oscillator tube and to improved systems incorporatingsuch tubes.

Known traveling wave tubes are electron discharge devices in which a gunassembly produces and accelerates an electron beam along a predeterminedpath toward a collector electrode upon which the beam terminates. Alongthe beam path, there is provided a slow wave-guiding or interactionstructure, generally in the form of a wire helix, through which theelectron beam passes; the wave-guiding structure carries radio frequencyenergy in substantial juxtaposition to the electron beam for interactionwith the electron beam. Appropriate radio frequency input and outputconnections are provided to the slow waveguiding structure and theentire traveling wave tube is normally immersed in a uniform axiallymagnetic field which serves to keep the electron beam from spreading dueto space charge effects. In such traveling wave tube devices one or moreelectrons moving in the electron beam interact with the same effectivephase of the moving electric field and energy is transferred between thebeam and the field. Many structures are known in the art for utilizingthis operating principle to obtain useful results in amplifiers andoscillators.

For example, in forward wave amplifier operation of a traveling wavetube, a radio frequency signal is placed on the helix at the inputconnection adjacent the electron gun and interaction takes place betweenthe radio frequency field and the electrons in the beam, the interchangein energy favoring an increase in the radio frequency amplitude for aparticular beam velocity. The output connection is at the collector endof the tube. Such structures may exhibit an amplitude gain for the radiofrequency signal which may be of the order of a thousand times orgreater the amplitude of the radio frequency input signal; the voltageat which maximum gain occurs for a given amplifier geometry is known inthe art as the synchronous voltage for the tube and the value generallyis given in specifying tube operation.

It is known in the art to operate traveling wave tubes as backward waveamplifiers. In such backward wave operation, interaction takes placebetween the electron beam which travels along a beam path from theelectron gun to the collector electrode and the backward wave spatialharmonic whose phase velocity moves in the forward direction and Whoseenergy travels in-;a direction opposite to the electron beam through theinteraction structure. It is characteristic of such backward waveamplifier tubes that the amplification or gain of the tube increaseswith increases in current flow in the electron beam adjacent to theinteraction structure which carries tially independent and remainsconstant despite the voltage variation.

For a given length oiinteraction structure, there is a ates atent valueof beam current designated as the start oscillation current at which thebackward wave tube has an infinite gain; at such start oscillationcurrent the flow of beam current will cause oscillation to occur and thebackward wave tube becomes essentially an electronically tunedoscillator. As the length of the interaction structure is increased, thestart oscillation current is decreased; and as the length of theinteraction structure is decreased the start oscillation is increased.As'is understood when the conventional backward wave tube operates as anamplifier the beam current is below the start oscillation current andthe gain of the tube increases with beam current up to the point wherethe start oscillation current is reached and the tube breaks intooscillation. It has been reported that above the start oscillationcurrent, gain is realized at the same frequency as the frequency ofoscillation.

Although conventional backward wave tube oscillators have found manyapplications, there are drawbacks in the practical utilization of suchtubes for both amplification and oscillation due to oscillator output atthe signal input end 6f the interaction structure. That is, unwantedoscillator power appears at the radio frequency signal input to theinteraction structure, which unwanted power may be the result ofimperfect microwave transistions of the tube, improper impedancematching and the like.

It is broadly an object of the present invention to provide a travelingwave tube of the backward wave type which is capable of simultaneousamplification and oscillation. Specifically, it is Within thecontemplation of the present invention to provide a backward waveamplifieroscillator tube which may be electronically tuned over a broadfrequency band.

It is a further object of the present invention to provide an improvedmicrowave device capable of functioning concurrently as an amplifier andoscillator which makes possible design of a wide variety of microwavetransmission systems, particularly those finding military application.To advantage, a combined amplifier-oscillator tube according to thepresent invention may find application in radar jamming devices, securetransmission radar, search receivers, and other commercial. and militarysystems.

In accordance with an illustrative embodimentidemonstrating features ofthe present invention, there is provided a traveling wave tube whichincludes means for projecting an electron beam along a predeterminedpath in one direction, an interaction structure including aforeshortened energy guide for transmitting input signal energy alongthe beam path in the opposite direction, and a region of concentratedattenuation along the length of interaction structure and intermediatethe ends thereof which divides the interaction structure into twolengths coupled together by the region of concentrated attenuation. Asignal input connection is provided to the length or region remote fromthe electron gun while a signal output connection is provided tothelength or section contiguous to the electron gun. The section orlength having the output connection is longitudinally longer than thesection or length having the input connection; accordingly the startoscillation current of the longer section is lower than the startoscillation current of the shorter section. By appropriate selection ofthe circuit parameters and of the respective lengths of the sections,the tube may be operated at abeam current which is above the startoscillation current for'the longer length section and below the startoscillation current for the shorter length section. Therefore, thelonger length section operates as an oscillator while the shorter lengthsection simultaneously operates as an amplifier; both of these sectionsare tuned by the common direct current voltage applied to theinteraction structure.

Although there are many practical applications of the present backwardwave amplifier-oscillator tube, there will be detailed hereinafter asearch receiver capable of locking onto an unknown radio frequency inputsignal. Briefly, such search receiver incorporates a backward waveamplifier-oscillator tube of the previously described construction, adetector coupled to the output connection of the tube, means for varyingthe magnitude of the direct current voltage applied to the interactionstructure whereby the common operating frequency of both the oscillatorand amplifier sections may be swept over a range of frequencies, andmeans responsive to output from the detector and controlling variationsin direct current voltage such that upon coincidence of the oscillatorfrequency and the unknown input signal the tube will be locked onto thefrequency of the unknown input sig nal. Such receiver illustrates butone of the many applications of the present combinedamplifier-oscillator tube serving in part as an electronically tunablebandpass filter. It will be appreciated that input radio frequenciessignals at a frequency other than the frequency of the oscillatorsection has little or no eifect upon the output level; however, as theinput signal frequency approaches the frequency of the oscillatorsection there is a rapid rise of output indicative of coin'cidencebetween the frequency of the local oscillator and that of the unknownsource.

The above brief description as well as further objects, features andadvantages of the present invention will be best appreciated byreference to the following detailed description of a combined backwardwave traveling tube amplifier-oscillator tube and an illustrative systemaccording to the present invention when taken in conjunction with theaccompanying drawings:

Fig. l is a schematic showing of a backward wave oscillator-amplifiertube embodying features of the present invention; and

Fig. 2 is a schematic diagram showing the combined backward waveoscillator-amplifier tube of Fig. 1 embodied in a search receiver.

Referring now specifically to Fig. 1 there is shown an envelopeincluding an elongated slender sleeve 12 and an enlarged bulb end orsection 14. Disposed within the bulb end is an electron gun 16 which isarranged to project a beam of electrons along a path axially of thesleeve 12 toward a collector electrode 18. The electron gun, which iswell known per se, includes a beam current controlling electrode 19, afocusing and accelerating electrode 20, a cathode 22 capable of emittingelectrons and a heater coil 24. Appropriate connections are provided forestablishing operating potentials for the several electrodes of the gunassembly 16 and for the collector electrode 18. Specifically, the heatercoil 24 is connected by leads 26, 28 to a heater supply (not shown); thefocusing and accelerating electrode is connected internally to theinteraction structure and both are connected via the lead 32 to thepositive side of the voltage source and the collector 18 is connectedvia lead 34 to an appropriate low voltage source 31 such thatunconverted portions of the kinetic energy of the beam appear as heat atthe collector electrode 18. The variable voltage source 30 appliesdirect current voltage between the interaction structure and thecathode.

Disposed within the sleeve 12 is the interaction structure, generallydesignated by the reference numeral 40, which in this embodiment isillustrated as a continuous wire helix extending between an inputconnection 42 and an output connector 44. Radio frequency connectionsare made to the opposite ends of the helix by appropriate input andoutput wave guide couplings, illustrated as the coaxially coupling 46connected to the input connection 42 and the coaxial coupling 48connected to the output connection 44. 7

In accordance with the present invention, the interaction structure isdivided into three separate sections or lengths by the provision of aregion 50 of concentrated attenuation intermediate the ends of theinteraction structure and extending for a predetermined length. Theregion of concentrated attenuation divides the interaction structureinto a first section 52 intermediate the radio frequency signal inputconnections 42, 46 and one end of the region 50 and a second section 54intermediate the other end of the region 50 and the radio frequencysignal output connections 44, 43. The section 54 which is of a length L3is longitudinally longer than the section 52 which is of the length Ll;thus it follows that the start oscillation current of the section islower than the start oscillation current of the section 52. Accordingly,it is possible to operate the traveling wave tube at a beam currentwhich is above the start oscillation current for the section 54 andbelow the start oscillation current for the section 52. It follows thatthe section 54 operates as an oscillator while the section 52 operatesas a backward wave amplifier, both sections 52, 54 being tuned by thecommon direct voltage applied to the interaction structure 40 which isof the length L1+LZ+L3. The oscillator frequency, as determined by thedirect current voltage 30 applied to the interaction structure 40,occurs slightly off the center of the passband for the oscillatorsection 54; this may be attributed to the fact that section 54simultaneously operates as an amplifier and oscillator and the center ofits amplifier passband exactly coincides with the oscillator frequency.The frequency at which the section 52 amplifies may be varied by varyingthe voltage applied to the traveling wave interaction structure 40 andis dependent upon the length L1 of the section 52. Thus the amplifiersection 52 operates at a frequency slightly off the frequency of theamplifier-oscillator section 54. However in that the gain of theamplifier-oscillator section 54 is much larger than that of theamplifier section 52 it is possible to design the tube such that maximumgain occurs substantially at the oscillator frequency.

The function of the attenuator section 50 is primarily to define theamplifier section 52 and the oscillator-arn plifier section 54. Furtherthe attenuator section 50 determines the amount of coupling between theinput and output sections 52, 54 of the backwardwave tube. Al-

though some of the radio frequency is lost in the attenuator section thecoupling may be made a maximum consistent with the required operationalcharacteristics of the present tube. Further, the concentrated region ofattenuation limits the amount of oscillator energy appearing at theinput connection 46. As a practical matter it is possible to obtain anearly ideal match looking into the attenuator 50 from either direction;with a reasonable amount of attenuation any changes in impedance at theinput connection negligibly effect the nearly ideal match as seenlooking into the attenuator section 50 from the oscillator section 54.Theoretically if the match is perfect there is no microwave field energyfrom the oscillator at the attenuator. However, as a practical matterimperfect match will occur at the output connection 48. For the smallamount of oscillator energy fed back to the attenuator section 50 as aresult of this imperfect match, the attenuator assures very littleoscillator output at the input connections 42, 46. Thus, it is possibleto minimize the oscillator field energy that can get to the radiofrequency input. oscillator section 54 and the amplifier section 52produce amplification and the attenuator section 50 in this respectfunctions much in the same way as a forward broad band amplifier toprevent oscillation resulting from feedback along the helix from outputto input due to mismatch at the output and input connections. It will beappreciated that two factors contribute to isolation of the oscillatorsection 54 from the input section, name- Still further both the ly, goodmatching of the attenuator and the value of the attenuator. As tocoupling signal power from input to output it is desirable to have theattenuator value or length as small as possible consistent with therequirements of isolation of the oscillation output from the radiofrequency input.

Details of experiments conducted with a backward waveoscillator-amplifier tube according to the present invention may furthercontribute to a thorough understanding of the present invention. In anexperimental tube the interaction structure was a molybdenum tape helixnine inches in length, that is L1+L2+L3 was equal to nine inches. Thetape size was .020 inch by .075 inch in cross section and was wound witha pitch of nine turns per inch. The outer diameter of the helix was .420inch and the inner diameter was .380 inch. The helix was contained in aprecision bore glass tube axial- 1y straight and of Corning 7052 glasswhose inner diameter was .420 inch and whose outer diameter was .500inch. The electron gun was a hollow beam type capable of deliveringabout twelve milliamperes. The hollow beam had an outer diameter of .357inch and inner diameter of .307 inch and was directed toward a cupshaped collector. The electron gun was of the immersion type and thusthe entire tube including the gun assembly was disposed within alongitudinal magnetic field to keep the beam collimated. The attenuatorsection 50 was formed by placing an aquadag coating external to theglass while each end of the helix was terminated in an appropriate broadband transistion to standard coaxial lines.

The experiments performed with the aforesaid tube were intended toillustrate operating principles rather than to indicate range or orderof magnitude of electrical characteristics. The tube under test wasactually converted from a conventional backward wave oscillator capableof delivering from between eleven to a hundred milliwatts output andhence data cannot be used to predict operation of low-level units, suchmicrowave receivers. Gain tests conducted with the start oscillationcurrent below value for oscillation of section 54 indicate that the tubeunder these conditions performs very much the same way as a conventionalbackward wave amplifier. As in a conventional backward wave amplifier,the closer the beam current is made to the start oscillation value, thehigher the backward wave gain. Operation as a backward waveoscillator-amplifier in accordance with the present invention resultedin tube output with the input pulses appearing as amplitude modulationof the carrier frequency of three thousand megacycles per second. Thisamplitude modulation can be made positive or negative by shifting thephase of the input signal and finds application where it is desirable toinvert the modulation of the input signal. Actual gain values could beobtained by detecting the signal output and comparing the detectedoutput with the signal input. Recalling that the backward waveoscillator-amplifier tube. of the present invention is electronicallytunable by varying the direct current voltage on the interactionstructure, it is evident that there is always an oscillator output at afrequency corresponding to the voltage applied to the interactionstructure. Only when the oscillator output frequency coincides with thecarrier frequency of the pulse signal input is maximum gain attained;thus the tube will have maximum gain at the same frequency as thefrequency of oscillation of the section 54.

In summary the following conclusions may be drawn with respect to theconducted experiments:

As to the relationship between gain and beam current, it was indicatedthat the gain increased as the beam current approached the startoscillation current whether the beam current was above or below thestart oscillation current. Below the start oscillation current the tubebehaved as backward amplifier; while above start i 6 oscillation currentthe tube operated as a backward wave amplifier-oscillator, amplifyingand oscillating simultaneously at the same frequency.

As to the relationship between gain and helix voltage response curvesindicate typical tuned amplifier operation with maximum gain occurringwhen the carrier frequency of the input impulses coincided with thebackward wave amplifier-oscillator frequency as controlled by thevoltage applied to the interaction structure.

As to the acceptance band which is a measure of the oscillationfrequency band for three db gain variation from maximum gain for a giveninput signal frequency, it was found that the acceptance band wasapproximately 1 to 5 megacycles wide depending upon beam current and theposition of the attenuating section 50.

As to band width which is a measure of the input signal frequency bandfor a three db gain variation from maximum gain for a given helixvoltage, the results show that the band widthwas of the order of 1 to 5megacycles wide depending upon beam current and attenuator position.

Reference will now be made to Fig. 2 wherein there is shown a searchreceiver embodying a combined traveling wave tube oscillator-amplifiertube according to the present invention which is capable of identifyingand storing the carrier frequency of the unknown radio frequency inputsignal. The receiver, generally designated by reference numeral includesa backward amplifieroscillator tube 102 as detailed in conjunction withFig. 1 which includes a signal input connection 104, a signal outputconnection 206 and a connection 108 to the interaction structure of thetube for varying the direct current voltage applied to the interactionstructure as a means for controlling the common operating frequencies ofthe amplifier and oscillator sections of the tube 302. Connected to theinput connection 104 is an antenna 110 which applies the unknown radiofrequency input signal to the input end of the interaction structure forbackward wave interaction. The output connection 106 is connected to adetector 112, which may be in the form of a crystal diode. The detectedoutput appearing on line 114 may be visually displayed on an appropriateoscilloscope such as illustrated at 116; further the detected output isused to control the sweeping of the oscillator frequency of the tube 102as determined by the variable direct current voltage applied on lead108. The variations in direct current voltage on the lead 108 areattained in the illustrative device through the provision of appropriatesweep supply 118 illustrated as including a source of direct currentvoltage 120 connected in circuit with a resistance 122 which is tappedby a rotating contact 124 connected to lead 108. The contact 124 ismoved along the resistance 122 by'a motor 126 having energizationconnections 128, 130. The energization circuit for the motor includes anormally closed switch 132 and a voltage source 134. The helix sweepsupply 118 is arranged to vary the voltage on the lead 108 continuouslyor as long as the switch 1322 remains closed and; when the switch 132 isopened the direct current voltage is of a magnitude determined byposition of the contactor 124 in relation to the resistor 122. For thispurpose, the output 114 of the detector is applied to an amplifier 136which has a relay 138 connected in its output circuit in controllingrelation to the switch 132. Upon output of the detector 112corresponding to coincidence between the unknown input frequency and thefrequency generated by the combined amplifier-oscillator tube 102, theamplifier 136 and relay 133 are effected to open the switch 132 thusinterrupting the voltage sweep for the interaction structure andcontinuing operation of the backward wave amplifier-oscillator tube 102at the unknown frequency. Appropriate identification friend or foeequipment and/ or radar jamming devices may be associated with thesearch receiver as is well understood in the art.

As previously stressed other applications of the combined backward waveamplifier-oscillator tube of the present invention are contemplated. Forexample, the present tube finds numerous applications in conjunctionwith combined traveling wave tube indicators of the type disclosed anddescribed in co-pending application Serial Number 275,539 in the name ofPhillipe Clavier and assigned to the assignee of the present invention.For example, general purpose radar receivers may be greatly simplifiedby incorporating a traveling wave tube amplifier and indicator accordingto the mentioned co-pending application and the backward wave travelingwave tube of the present invention. Not only is the radar receiverconfiguration considerably simplified but further the functions ofseveral mixers and local oscillators are combined effecting substantialreductions in the number of tubes and associated circuits.

I claim:

1. A traveling wave tube comprising means or projecting an electron beamalong a predetermined beam path and in one direction, an interactionstructure including input and output connections and a foreshortenedenergy guide for transmitting input signal energy along said beam pathin the opposite direction, and a region of concentrated attenuationalong the length of said interaction structure intermediate said inputand output connections dividing said interaction structure into twosections coupled together, the section adjacent said output connectionbeing of a length greater than the other of said sections.

2. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, guide means adjacent to andalong said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun,attenuating means along an intermediate portion of said guide meansdividing said guide into two parts coupled together by said attenuatingmeans, the part adjacent said electron gun serving with the coextensivepart of said tube to provide a backward wave oscillator-amplifiersection, the part adjacent said collector electrode being shorter thansaid first named part and serving with the coextensive part of said tubeto provide a backward wave amplifier section.

3. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, a helix adjacent to and alongsaid beam path for propagating an input signal along said beam path inthe direction fro-m said collector electrode to said gun, attenuatingmeans along an intermediate portion of said helix dividing said helixinto two parts coupled together by said attenuating means, the partadjacent said electron gun serving with the coextensive part of saidtube to provide a backward wave oscillator-amplifier section, the partadjacent said collector electrode being shorter than said first namedpart and serving with the coextensive part of said tube to provide abackward wave amplifier section.

4. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, guide means adjacent to andalong said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun,attenuating means along an intermediate portion of said guide meansdividing said guide means into two parts coupled together by saidattenuating means, the part adjacent said elec.ron gun serving with thecoextensive part of said tube to provide a backward waveoscillator-amplifier section, the part adjacent said collector electrodebeing shorter than said first named part and serving with thecoextensive part of said tube to provide backward wave amplifiersection, means for establishing the beam current of said tube at a valueabove the start oscillation current for said oscillator-amplifiersection and below the start oscillation current for said amplifiersection,

8 and means for applying a varying direct current voltage to said guidemeans whereby the common operating frequency of said sections may bevaried over a range.

5. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, guide means adjacent to andalong said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun,attenuating means along an intermediate portion of said guide meansdividing said guide means into two parts coupled togetner by saidattenuating means, the part of said guide means adjacent said electrongun serving with the coextensive part of said tube to provide a backwardwave oscillator-amplifier section, the part of said guide means adjacentsaid collector electrode being shorter than said first named part andserving with the coextensive part of said tube to provide a backwardwave amplifier section, means for applying signal input of unknownfrequency to said amplifier section, a detector circuit deriving inputfrom said amplifier-oscillator section, means for tuning saidamplifier-oscillator section through a frequency range including saidunknown frequency, and means controlled from the output of said detectorfor interrupting tuning of said amplifier-oscillator section when thelatter is operating at a frequency substantially equal to said unknownfrequency.

6. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, a continuous helix adjacent toand along said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun,attenuating means along an intermediate portion of said helix dividingsaid helix into two lengths coupled together by said attenuating means,the length adjacent said electron gun serving with the coextensive partof said tube to provide a backward wave oscillator section, the lengthadjacent said collector electrode being shorter than said first namedlength and serving with the coextensive part of said tube to provide abackward wave amplifier section, means for applying signal input ofunknown frequency to said amplifier section, a detector circuit derivinginput from said oscillator section, means for tuning said oscillatorsection through a frequency range including said unknown frequency, andmeans controlled from the output of said detector for interruptingtuning of said oscillator section when the latter is operating afrequency substantially equal to said unknown frequency.

7. A traveling wave tube device comprising means for projecting anelectron beam along a predetermined beam path and in one direction, aninteraction structure including a foreshortened energy guide fortransmitting input signal energy along said beam path in the oppositedirection, a region of concentrated attenuation along the length of saidinteraction structure and intermediate the ends thereof dividing saidinteraction structure into an amplifier section and an oscillatorsection, a signal input connection to said amplifier section, a signaloutput connection from said oscillator section, means for sweeping theoperating frequency of said sections through a range of frequencyvalues, detector means receiving signal output from said oscillatorsection, said detector providing a control signal when the operatingfrequency corresponds substantially to the frequency of the signal inputto said amplifier section, and means responsive to said control signalfor interrupting the frequency sweep of said sec tions.

8. A traveling wave tube device comprising means for projecting anelectron beam along a predetermined beam path and in one direction, aninteraction structure including a helix for transmitting input signalenergy along said beam path in the opposite direction, a region ofconcentrated attenuation along the length of said helix and intermediatethe ends thereof dividing said helix into a first length serving in anamplifier section and a second length serving in an oscillator section,a signal input connection to said amplifier section, a signal outputconnection from said oscillator section, means for sweeping theoperating frequency of said sections through a range of frequencyvalues, detector means receiving signal output from said oscillatorsection, said detector providing a control signal when the operatingfrequency corresponds substantially to the frequency of the signal inputto said amplifier section, and means responsive to said control signalfor interrupting the frequency sweep of said sections.

9. A search receiver capable of identifying and storing an unknown inputsignal comprising a backward wave amplifier-oscillator tube including anelectron gun and a collector electrode defining a beam paththerebetween, an interacting structure including transmission meansadjacent to and along said beam path for propagating an input signalalong said beam path in the direction from said collector electrodetoward said gun, input means including an antenna coupled to saidtransmission means adjacent said collector electrode for applying saidinput signal to said transmission means and output means coupled to saidtransmission means adjacent said gun for removing said electromagneticwave therefrom, a detector deriving its input from said output means,attenuating means along said beam path intermediate said input andoutput means and dividing said interaction structure into an amplifiersection intermediate said input means and one end of said attenuatingmeans and into an oscillator section intermediate the other end of saidattenuating means and said output means, said oscillator section beinglonger in length than said amplifier section, said tube being operatedat a beam current below the start oscillation current for said amplifiersection and above the start oscillation current for said oscillatorsection, means for applying varying direct current voltage to saidtransmission means, the instantaneous magnitude of said voltagedetermining the common operating frequency of said sections, means forvarying the magnitude of said direct current voltage whereby the commonoperating frequency may be swept over a range of frequencies, and meansresponsive to the output from said detector and controlling the meansfor varying said direct current voltage.

10. A backward wave amplifier-oscillator tube comprising means providingan electron beam in a forward direction along a beam path, aninteraction structure adjacent to and along said beam path forpropagating an electromagnetic wave in a backward direction along saidbeam path, input means coupled to said interaction structure forapplying an electromagnetic wave to said interaction structure forpropagation in the backward direction, output means coupled to saidinteraction structure for removing said electromagnetic wave therefrom,attenuating means along said interaction structure intermediate saidinput and output means dividing said interaction structure into a firstsection capable of operation as a backward wave oscillator-amplifier anda second section capable of operation as a backward'wave amplifier, andmeans for operating said tube at a beam current above the startoscillation current for said first section and below the startoscillation current for said second section.

11. A traveling wave tube comprising means including an electron gun forprojecting an electron beam along a predetermined beam path and in onedirection, an interaction structure including a foreshortened energyguide for transmitting input signal energy along said beam path in theopposite direction, attenuating means along the length of saidinteraction structure and intermediate the ends thereof dividing saidinteraction structure into two sections coupled together in an amountdetermined by the magnitude of said attenuation, one of said sectionsbeing adjacent said electron gun and of a length greater than the otherof said sections, means for applying a signal input to the other of saidsections and for extracting signal output from said one section, andmeans for establishing a beam current above the start oscillation '10current for said one section and below the start oscillation current forsaid other section.

12. A traveling wave tube device comprising means for projecting anelectron beam along a predetermined beam path and in one direction, aninteraction structure for transmitting input signal energy along saidbeam path in the opposite direction, attenuating means along the lengthof said interaction structure and intermediate the ends thereof dividingsaid interaction structure into an amplifier section and an oscillatorsection, a signal input connection to said amplifier section, a signaloutput connection from said oscillator section, means for sweeping theoperating frequency of said sections through a range of frequencyvalues, means receiving signal output from said oscillator section andproviding a control signal when the operating frequency correspondssubstantially to the frequency of the signal input to said amplifiersection, and means responsive to said control signal for interruptingthe frequency sweep of said sections.

13. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, guide means adjacent to andalong said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun,attenuating means along an intermediate portion of said guide meansdividing said guide means into two parts coupled together by saidattenuating means, the part of said guide means adjacent said electrongun serving with the coextensive part of said tube to provide a backwardwave oscillator section, the part of said guide means adjacent saidcollector electrode being shorter than said first named part and servingwith the coextensive part of said tube to provide a backward waveamplifier section, means for applying signal input of unknown frequencyto said amplifier section, a traveling wave tube indicator derivinginput from said amplifier-oscillator section, and means for tuning saidamplifier-oscillator section through a frequency range including saidunknown frequency.

14. In combination with a tube including an electron gun and a collectorelectrode defining an electron beam path, guide means adjacent to andalong said beam path for propagating an input signal along said beampath in the direction from said collector electrode to said gun, meansalong an intermediate portion of said guide means establishing withinsaid tube a backward wave oscillator section and a backward waveamplifier section, means for applying signal input of unknown frequencyto said ampllfier section, a traveling wave tube indicator derivinginput from said amplifier-oscillator section, and means for tuning saidamplifier-oscillator section through a frequency range including saidunknown frequency.

15. A traveling wave tube device comprising means for projecting anelectron beam along a predetermined beam path and in one direction, aninteraction structure for transmitting input signal energy along saidbeam path in the opposite direction, attenuating means along the lengthof said interaction structure and intermediate the ends thereof dividingsaid interaction structure into an amplifier section and an oscillatorsection, a signal input connection to said amplifier section, a signaloutput connection from said oscillator section, means for sweeping theoperating frequency of said sections through a range of frequencyvalues, and means receiving signal output from said oscillator sectionand providing a control signal when the operating frequency correspondssubstantially to the frequency of the signal input to said amplifiersection.

References Cited in the file of this patent UNITED STATES PATENTS

